Not Applicable.
Not Applicable.
1. Field of the Invention
The present invention relates generally to display devices and, more particularly, to two-dimensional beam scanners.
2. Description of the Invention Background
Varying the direction at which a beam is projected has been accomplished in various ways. A basic method for redirecting a beam is to move the source of the beam. When complex or high speed motion is required, however, this method becomes impractical because of the size of the source and the electrical connections that must be maintained to power the beam.
Mechanical beam scanning systems, such as spinning polygon mirrors, have been used to reflect a beam onto a two-dimensional display plane. Scanning along both the X and Y axes of the two-dimensional display plane is generally accomplished by the use of two such polygonal mirrors. The first mirror moves about one axis to scan the beam in the direction perpendicular to the axis. The beam impinges on the first mirror which varies the position and angle of incidence of the beam on the second mirror. The second mirror moves about a second axis, orthogonal to the axis of the first mirror, to scan the beam orthogonally to the scan direction of the first mirror. Spinning mirrors can be troublesome because they require large mechanisms to move the mirrors. To achieve high scanning speed, larger, more costly and less controllable drives typically must be coupled with multifaceted mirrors. High scanning speed can be further limited by deformation of the mirror, due to centrifugal forces, and motor bearing limitations. The use of less controllable drives and the deformation of the mirrors can also result in reduced beam placement accuracy. Therefore, high scanning speed in mechanical scanners is generally achieved at the cost of reduced accuracy. Additional distortions are also introduced into the projected beam because the facets of the spinning mirrors cannot be perfectly ground.
Spinning mirrors are also sequential devices, incapable of displaying discrete points without progressively moving the beam across the display plane from a first point to a second point. Progressive beam movement is inherent in spinning mirrors because spinning mirrors must be turned from one position to another over time, thereby scanning the beam across all intermediate display points and forming a line between the desired display points. Spinning mirrors, therefore, cannot be instantaneously adjusted to display the beam on any display plane point.
Non-mechanical beam scanners have been utilized to vary the direction of a beam but have not been effectively applied in two-dimensional beam scanning applications. Non-mechanical beam scanners vary the direction at which a beam of light, incident on the beam scanner""s input surface, is output from the beam scanner""s output surface. Non-mechanical beam scanners deflect a beam with no physical movement of the scanner. It is a characteristic of non-mechanical beam scanners to vary the amount of deflection as a function of acoustic, electric, thermal, or other form of energy applied to the scanner. Non-mechanical scanners are advantageous because they are comparatively small and easily portable and do not have moving parts to wear or fail.
In one embodiment of an electro-optic beam scanner disclosed in U.S. Pat. No. 5,317,446 to Mir et al., the angle of beam deflection is dependent on an electric field applied to an electro-optic prism array. The electrical field polarizes the prism array, thereby deflecting the beam in a single plane. The degree of deflection of the beam is infinitely adjustable and may be controlled by controlling the level of the electrical field applied. Acousto-optic and thermo-optic beam scanners have also been developed. In an acousto-optic beam scanner, the angle of deflection of the beam may be controlled by controlling an acoustic field applied to the optic material. In a thermo-optic beam scanner the angle of deflection of the beam may be controlled by controlling the temperature of the optic material.
Some non-mechanical beam scanners are capable of deflecting a beam in a single plane so that the beam output therefrom is capable of forming a line on a two-dimensional display plane. There is a need, however, to have more complicated shapes projected in two dimensions. U.S. Pat. No. 4,925,261 to Byckling et al. suggests that two beam scanners be placed in series such that the first beam scanner deflects the beam in the X-direction and the second beam scanner deflects the beam in the Y-direction. The problem with that method is the difficulty of creating a beam scanner that is capable of receiving a beam over a significant range of input points corresponding to output points of the first scanner in the series. Beam scanners are typically constructed with beam input and beam output surfaces that are broad in the plane in which the beam is deflected and thin in the perpendicular direction. That is because broad, thin sections of optic material are easy to polarize and thus capable of precise control over large angles of deflection. Thick sections of optic material require greater amounts of power to polarize and are difficult to uniformly polarize. Therefore, optic material is kept thin to minimize power requirements and maximize controllability. To accept a beam at any number of planes displaced in a direction perpendicular to the deflection plane would require that the optic material be thick enough to accept the full range of potential output positions of the first beam scanner. That, in turn, increases the power required to deflect the beam through a thicker crystal and makes it-more difficult to control the amount of deflection.
U.S. Pat. No. 4,902,088 to Jain et al. presents a single beam scanner scanning in only the X direction which is incident on holographic facets. The beam is intended to be incident on a single holographic facet at a time. Each holographic facet is capable of changing the direction of the beam in both the X and Y directions. That apparatus is thereby capable of creating a two-dimensional display. That apparatus, however, has the limitation that each point of incidence on the facets has only one possible Y direction of diffraction.
U.S. Pat. No. 4,902,088 to Jain et al. also presents a single beam scanner scanning in only the X direction which is incident on multiple diffraction gratings. In that configuration each diffraction grating may be separately energized such that each point of incidence on the diffraction gratings may be directed to a single point in the Y direction for each grating present in the apparatus. That apparatus has the limitation that each point of incidence on the diffraction gratings may only be refracted to a number of points in the Y direction equal to the number of diffraction gratings present.
Accordingly, a need exists for an infinitely adjustable, cost effective, non-mechanical beam scanner and a method for projecting a beam onto a display plane in two-dimensions.
The present invention is directed broadly to a device comprised of a projection element having an intermediate surface, first and second beam scanners configured in series, a two-dimensional display plane and an apparatus for controlling the first and second beam scanners. The two beam scanners are for receiving an input beam and outputting an output beam so as to vary an angle of incidence of the output beam with respect to the intermediate surface and a point of incidence of the output beam on the intermediate surface. The two-dimensional display plane is provided to receive a beam projected from the intermediate surface. The device also includes an apparatus that controls the beam scanners such that each point of incidence on the intermediate surface maps to a line on the two-dimensional display plane by varying the angle of incidence.
The present invention is also directed to a method of projecting a beam onto a two-dimensional display plane. The method includes passing a beam through series configured beam scanners to produce an output beam and controlling both the angle of incidence of the output beam with-respect to an intermediate surface and the point of incidence on the intermediate surface. The angle of incidence and the point of incidence determine the path of a beam projected from the intermediate surface onto the two-dimensional display plane.
The present invention offers the advantage of varying the position of a display point, arbitrarily, and at high speed. It allows unlimited variation on a two-dimensional display plane in both the X and Y directions. The present invention is small and portable, having no moving parts to wear or fail, and it functions using beam scanners that require minimal power and are easily controllable. Those advantages and benefits, and others, will become apparent from the Detailed Description of the Invention hereinbelow.